1. Field of Invention
The present invention relates to a drowsy state determination device and method, and more specifically to a device and method that determines the drowsiness level of the driver of a mobile unit such as an automobile.
2. Description of Related Art
In recent years, there have been proposed devices that determine the drowsiness level of the driver of a mobile unit such as an automobile (see Japanese Patent Application Publication No. 6-219181 (JP-A-6-219181), for example). The doze detector disclosed in JP-A-6-219181 accumulates the duration of blinks (hereinafter referred to as “eye closures”) of the driver of a prescribed time or more over a fixed period. The doze detector determines that the driver is dozing when the accumulated duration exceeds a predetermined threshold.
The above doze detector compares the accumulated duration of all the eye closures that last for the prescribed time or more over the fixed period with the threshold to determine whether the driver is awakened or dozing. The drowsiness level of the driver, however, cannot be simply differentiated into two states, namely awakened and dozing. Rather, the drowsiness of the driver can be differentiated into more than two levels including, for example, slight drowsiness and heavy drowsiness. That is, the drowsiness level of the driver can be differentiated into more than two drowsiness levels ranging from awakened to dozing, which corresponds to the heaviest drowsiness. The duration of eye closures of the driver vary greatly among different drowsiness levels.
Therefore, the doze detector may erroneously determine that the driver is dozing, even in the case where the driver is actually awakened, once the driver closes his/her eyes for a period indicated by the threshold or more, even if the threshold for comparison with the accumulated duration is set optimally. Such an erroneous determination can be made when, for example, the driver is so dazzled by a bright light in the surroundings, such as a backlight, that he/she narrows or closes his/her eyes. In addition, since the drowsiness level of the driver is simply differentiated into two levels, namely awakened and dozing, the doze detector may erroneously determine that the driver is simply dozing, even in the case where the driver is actually feeling slight drowsiness or heavy drowsiness. That is, the above doze detector has a problem of erroneously determining the drowsiness level of the driver.